Our objectives are as follows: (1) To determine the amount of polymorphism in genes coding for different types of polypeptides in natural populations of Drosophila (2) To determine the nature and extent of genetic changes that accompany different stages of speciation (3) To determine the adaptive significance of allele polymorphism. We will examine allelic variation at various monomorphic and moderately polymorphic loci in D. pseudoobscura, reproductively isolated Bogota (Colombian) population and the closely related species D. persimilis and D. miranda. Allelic variants will be distinguished by gel electrophoresis of proteins and enzymes in gels of different concentrations and different pH's. Allelic variants coding for polypeptides with different conformations will be distinguished by determination of retardation coefficients. Polymorphism in allozymes due to different numbers of cysteine residues with free sulfhydryls will be determined by reacting the allozyme with thiol reagents and determining their electrophoretic mobility. In addition, we will study activities of allozymes and stabilities as determined by heat and urea denaturation. Genetic analysis will be done with any newly discoveredg variants. Kinetic studies will be carried out with purified amylase and xanthine dehydrogenase allozymes affecting activity. Associations between the activity of xanthine dehydrogenase allozymes and the amount of drosopterin eye pigment will be studied by examining co-segregation of activity and drosopterin amounts with the xanthine dehydrogenase alleles. Population cage experiments with and without the substrates of the enzyme will be done in order to observe gene frequency changes in alleles coding for allozymes with different activities.